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The jury in the trial of two women accused of attempting to kill a 19-year-old in the Dome Valley will begin deliberating on Monday.

Nicola Jones and Julie-Ann Torrance are standing trial in the High Court at Auckland accused of kidnapping and sexually violating the woman, before leaving her for dead on a remote highway north of Auckland in May last year.

Co-accused Wayne Blackett admitted to attempted murder at the start of the trial and the Crown says Jones and Torrance laughed and egged him on as he tried to snap the young woman's neck and beat her head repeatedly with a hammer on the roadside where she was found.

Prosecutors say the day prior, the women, along with Michelle Blom, grabbed the complainant off Auckland's Karangahape Road, before locking her in the basement of Blom's Great North Road home and subjecting her to a prolonged attack.

Before the jury retired for the weekend on Friday, Justice Christian Whata took the court through a lengthy summary of the complex case.

He warned the jurors to put aside any prejudice they may have about prostitution, drug dealing and methamphetamine - themes throughout the trial.

Justice Whata said while the jurors may have felt sympathy for the complainant, they had to consider the accuracy of her evidence, given she was under extreme stress during the attacks and had been left with memory problems.

"Her injuries, to her head, are a factor when assessing her reliability, especially on matters on detail," he said, instructing jurors to disregard the woman's evidence about identifying Blom by voice during the basement attack.

The jury will begin its deliberations proper on Monday morning.

Blom's defence says there's no objective evidence she had taken part in the assault, while Jones' and Torrance lawyers told the court the complainant's evidence was unreliable and had changed over time.

Prosecutors say Jones, a close friend of the complainant, threatened to kill her in a text message after a dispute over an ex-boyfriend months before the attack - but defence lawyer Maria Pecotic said the message was just an emotional outburst.

A fifth accused, Cameron Hakeke, is charged with kidnapping and assaulting the young woman during an separate attack in April, over which Torrance and Jones also face charges.

His lawyers say he was out for work at the time of the attack and had no idea there had even been a kidnapping.